SQL Server 2012 查询混乱

Question

我是 SQL 的初学者，我似乎无法针对这个问题提出正确的查询：

使用相关子查询 return 每个客户一行，代表客户最早的订单（日期最早的订单）。每行应包括以下三列：EmailAddress、OrderID 和 OrderDate。

我从加入订单和客户开始 table。 EmailAddress 是客户 table.

唯一需要的列

      SELECT EmailAddress, OrderDate, orderID
      FROM Customers c JOIN orders o
      ON c.CustomerID = o.CustomerID

Answer 1

使用 ROW_NUMBER() 获取按 OrderDate 降序订购的每个客户的唯一 ID。最晚日期为 RNO=1。现在在外部查询中进行过滤。

SELECT EmailAddress, OrderDate, orderID
FROM
(
   SELECT ROW_NUMBER() OVER(PARTITION BY c.CustomerID ORDER BY OrderDate DESC)RNO,
   EmailAddress, OrderDate, orderID
   FROM Customers c JOIN orders o
   ON c.CustomerID = o.CustomerID
)TAB 
WHERE RNO=1

Answer 2

对于这个特定问题，您仍然可以使用 HAVING 子句和 IN 运算符来获得相同的结果

代码：

SELECT DISTINCT EmailAddress, OrderID, OrderDate
FROM Customers
    JOIN orders
    ON Customers.CustomerID = Orders.CustomerID
GROUP BY EmailAddress, OrderID, OrderDate
HAVING OrderID IN (1,2,4,5,6,7,8)
ORDER BY EmailAddress ASC;

Answer 3

一个不太复杂的答案：

SELECT  EmailAddress, OrderID, OrderDate AS OldestOrder
  FROM  Customers AS C
        JOIN Orders AS O1
            ON C.CustomerID = O1.CustomerID
 WHERE  O1.OrderDate =
            (SELECT MIN(OrderDate)
             FROM Orders AS O2
             WHERE C.CustomerID = O2.CustomerID)

SQL Server 2012 查询混乱

SQL Server 2012 Query Confusion

sql-server-2012